Add /usr/local/bin to wpcron PATH

Needed to find wp-cli, a dependency of noblogs-cli.

docker/conf/services.d/wpcron/run

 #!/bin/sh
+
 # Run WP-Cron periodically.
+
+# Need to be able to find wp-cli in /usr/local/bin
+export PATH=$PATH:/usr/local/bin
+
 # The "run-cron" execution takes a few minutes, so the actual period
 # comess out at something closer to 10 minutes.
 export BATCH_SIZE=300
-exec nice ionice -c 3 every 300 on-local-blogs run-cron >/dev/null
 
+exec nice ionice -c 3 every 300 on-local-blogs run-cron >/dev/null